Protein Content or Protein Composition: Which Is More Informative of Malting and Brewing Potential

Abstract: Cereals and their respective malts used in brewing and some distilled products, have a mix of complex chemistries. For decades, industries have used protein content as a surrogate measure of grain quality, and how a type of grain should perform in malting, mashing and in some downstream processing. But within the total protein content, there are 1000s of individual proteins, some of which are of little consequence in processes as they are residual proteins leftover from grain development. However, there is a small group of proteins that are critical for malting, mashing and in some cases, downstream quality. Instead of total protein content, the mix of water and alcohol soluble protein fractions would start to provide a greater picture of protein composition. Specifically in barley, the alcohol-soluble fraction contains the major endosperm storage proteins, ie. the hordeins, which are targeted for hydrolysis during malting. The alcohol-soluble fraction can make up from 40% to70% of the total protein and this is driven mostly by the growing environment and can indicate the potential modification of barley malt and impacts the swelling properties of starch granules. The water-soluble fraction contains globular proteins and enzymes. To fully understand the mix of alcohol and water soluble proteins which is comprised of 1000s of proteins is using proteomics, a technology that allows researchers to observe the abundance of all proteins expressed during grain development. The ratios of the major endosperm proteins including hordeins, beta-amylase, serine proteinase inhibitors and hordoindolines can be explored using proteomics and how these ratios relate to total protein content and grain quality. The overall abundance of these proteins is influenced by mostly the growing environment. The data shows an opportunity for industry to advance from a methods decades old (total protein content), and use modern proteomics to better understanding grain quality.